Polar bears in the high Arctic live on the permanent pack ice, following it as it recedes north in the warmer months (July to late September). These bears are able to roam and hunt for food throughout the year. Farther south, polar bears stay on the drifting ice and as it breaks up in summer, they come ashore. These southern bears must build up a huge fat reserve during the winter so that they can endure four months of fasting throughout the summer.